Refining and concentrating crude unsaturated aldehydes by extractive distillation



-ing means.

Patented July 11, 1950 REFINING AND CONCENTRATING CRUDE UNSATURATEDALDEHYDES BY EX- TRACTIVE DISTILLATION Delaware Application January 9,1948, Serial No. 1,314

This invention relatesto the production of 7 high purity unsaturatedaliphatic aldehydes from hydrocarbon oxidation products comprising theunsaturated aldehydes in admixture with close boiling saturatedcarbonylic compounds inseparable therefrom by practical scalefractionat- The invention relates more particularly to the separation ofalpha-beta unsaturated aliphatic aldehydes in a state of high purityfrom mixtures comprising the unsaturated aldehydes in admixture withsaturated aldehydes and/or ketones having the same number of carbonatoms as said unsaturated aldehydes. Still more particularly theinvention relates to the production of acrolein in a state of highpurity from mixtures comprising acrolein in admixture withpropionaldehyde and/or acetone.

Production of the unsaturated aldehydes on a practical scale generallyresults in the obtaining of a crude product comprising the unsaturatedaldehydes in admixture with substantial amounts of by-productsunavoidably formed during the process. The ability to utilize theunsaturated aldehyde efficiently in many of its fields of application isoften dependent upon the absence therein of any substantial amount ofimpurities. The large scale production of an unsaturated aldehyde ofrelatively high purity is, of necessity, limited to methods enabling theobtaining of a product comprising the unsaturated aldehyde in admixturewith impurities which are readily separable therefrom by availablepractical scale separating means. Thus the production of acrolein .fromsuch starting materials as, for example, acetaldehyde and formaldehydeunder carefully controlled conditions often enables the attainment of aproduct comprising the acrolein in admixture with impurities consistingessentially of acetaldehyde, formaldehyde and relatively high boilingorganic materials. All of such impurities are readily separable from theacrolein on a-practical scale by methods available heretofore comprisingsuch steps as simple fractionation, water scrubbing, distillation andthe like. Although acrolein of relatively high purity is often obtainedby such methods these processes are generally handicapped byunavailability at sufliciently low cost of the starting materials. Aparticularly valuable source of the unsaturated aldehydes comprises theproducts obtained by the oxidation of the readily availablehydrocarbons. It has recently been found that the readily availableolefinic hydrocarbons can be converted efliciently to productsconsisting predominantly of un- 16 Claims. (Cl. 202-395) saturatedaldehydes such as, for example, the alpha-betaunsaturated aliphaticaldehydes, by catalytic oxidation in the presence of specific catalysts.Thus acrolein is obtained by the catalytic oxidation of propylene.obtained in such catalytic hydrocarbon oxidations, however, comprisebesides the desired unsaturated aldehydes, saturated carbonyliccompounds such as, saturated aldehydes and ketones inseparable therefromon a practical scale by methods disclosed heretofore. The production ofan alpha-beta unsaturated aliphatic aldehyde from the correspondingolefin, such as, for example, the production of acrolein from propyleneresults in the production of a product comprising the acrolein inadmixture not only with readily separable impurities such as highboiling material, formaldehyde and acetaldehyde, but also close boilingcarbonylic compounds such as, for example, propionaldehyde and acetone,inseparable therefrom on a practical scale by separating means availableheretofore. Inability to effect the eflicient and yet substantiallycomplete removal of close boiling carbonylic compounds from theunsaturated aldehydes has militated against any full realization of thesubstantial advantages inherent in the utilization of the readilyavailable hydrocarbons as a source of these highly desirable andvaluable compounds.

It is an object of the present invention to provide an improved processfor the more eificient purification of the crude unsaturated aliphaticaldehydes obtained by the oxidation of hydrocarbons.

Another object of the invention is the provision of an improved processfor the more efiicient purification of crude alpha-beta unsaturatedaliphatic aldehydes obtained by the oxidation of the correspondingolefini'c hydrocarbon.

A more particular object of the invention is the provision of animproved process for the more eflicient purification of the crudeacrolein obtained by the catalytic oxidation of propylene.

A further object of the invention is the provision of an improvedprocess for the more efficient separation of an aliphatic unsaturatedaldehyde from admixture with saturated carbonylic compounds not readilyseparable therefrom by practical scale fractionating means.

Another object of the invention is the provision of an improved processfor the more eflicient separation of an alpha-beta unsaturated aliphaticaldehyde from admixture with saturated carbonylic compounds having thesame number of carbon atoms to the molecule.

The products .with. a saturated aliphatic aldehyde and/or ketone havingthe same number of carbon atoms I to the molecule.

A particular object of the invention is the provision of an improvedprocess enabling the more efllcient separation of acrolein from mixturescomprising acrolein in admixture with propionaldehyde and/or acetone.Other objects and advantages of the invention will become apparent fromthe following detailed description thereof.

In co-pending application Serial No. 49,816, filed September 17, 1948,there is described and claimed a method enabling the production of anunsaturated aldehyde of relatively high purity from a crude unsaturatedaldehyde containing saturated carbonylic impurities having boilingtemperatures closely approximating that of the unsaturated aldehyde, bysubjecting the crude material to two consecutive extractivedistillations in the presence of a suitable solvent. It has now beenfound that an unsaturated aldehyde, such as, for example, an alpha-betaunsaturated aliphatic aldehyde, is obtained in a high state of puritywith substantially improved efficiency from the crude unsaturatedaldehydes comprising it in admixture with saturated carbonylicimpurities having boiling temperatures closely approximating that of theunsaturated aldehyde by a method of purification employing a single lowtemperature extractive distillation step in the presence of a specificsolvent under well-defined conditions. The process of the inventionenables the separation of the unsaturated aliphatic aldehyde fromadmixed saturated carbonylic impurities including saturated ketones andsaturated aldehydes having the same number of carbon atoms to themolecule as the unsaturated aldehyde, in a single low temperatureextractive distillation. The single extractive distillation step of theprocess furthermore enables the simultaneous removal of any water fromthe unsaturated aldehyde to a greater degree than possible by ordinaryfractionating conditions.

The process of the invention may be applied broadly to the separation ofan unsaturated aldehyde from a mixture comprising it in admixture withsaturated aldehydes and ketones having the same number of carbon atomsto the molecule as the unsaturated aldehyde regardless of the source ofthe mixture. Because of its ability to effect in a single extractivedistillation the substantially complete removal from an unsaturatedaldehyde a plurality of close boiling saturated carbonylic impurities,such as saturated ketones and saturated aldehydes having the same numberof carbon atoms to the molecule as the unsaturated aldehyde as well aswater, the process of the inventions is applied with particularadvantage to the purification of the crude unsaturated aldehydes, suchas the alpha-beta unsaturated aldehydes obtained by the oxidation of thecorresponding hydrocarbons.

In accordance with the process of the invention a crude unsaturatedaliphatic aldehyde, such as a crude alpha-beta unsaturated aliphaticaldehyde containing close boiling saturated car- .bonylic impuritiescomprising saturated aldehydes and ketones having the same numberoxidation of propylene and containing propionaldehyde and acetone, issubjected to extractive distillation at a temperature below about (35C2) in the presence of a suflicient amount of water to maintain a singleliquid phase in the extractive distillation zone. It has been found thatunder the above-defined conditions substantially all of the saturatedcarbonylic impurities including the unsaturated aldehydes and ketoneshavin the same number of carbon atoms to the molecule as the unsaturatedaldehyde are removed as bottoms from the extractive distillation zonetogether with the water. Overhead from the extractive distillationconsists essentially of the unsaturated aldehyde free not only of anysubstantial amount of saturated carbonylic impurities inseparabletherefrom on a practical scale by methods disclosed heretofore, butcontaining substantially less water than comprised in the unsaturatedaldehyde-water azeotrope obtained under normal fractionating conditions.

In order that the invention may be more readily understood it will bedescribed in detail herein in its application to the production ofacrolein of high purity from crude acrolein obtained by the catalyticoxidation of propylene. Reference will be had to the accompanyingdrawings wherein Figure I illustrates more or less diagrammatically oneform of apparatus suitable for executing the process of the invention,and Figure II illustrates graphically the variation of the relativevolatility of acrolein-propionald'ehyde, acrolein-acetaldehyde, andacrolein-acetone mixtures, with variations in temperaturein the presenceof 83% by weight water.

When the alpha-beta unsaturated aliphatic aldehyde-containing mixture tobe purified in accordance with the invention consists essentially of amixture such as that eliminated from a reaction zone wherein theunsaturated aldehyde is produced by oxidation of the. correspondinghydrocarbon, the charge is first freed of at least the greater part ofnormally gaseous and relatively high boiling components prior to itspassage to the extractive distillation zone of the process. Referring toFigure I of the drawings, a crude acrolein-containing mixture consistingessentially of the eflluence from the reaction zone wherein it wasproduced by the catalytic oxidation of propylene, and optionallyemanating directly from such reaction zone, is passed through line l0into a separating zone. When the charge emanates directly from thereaction zone and is at an elevated temperature it is preferably passedthrough suitable cooling means, such as, for example, a cooler H.Optionally additional cooling means comprising the addition of aquenching medium, such as water to the stream by means of valved linel2, may be employed.

The propylene oxidation product will comprise besides the crude acroleincontaining the acrolein in admixture with acetaldehyde, acetone,propionaldehyde and water, certain amounts of formaldehyde, high boilingorganic materials, and substantial amounts of normally gaseousmaterials. The normally gaseous materials will comprise unconvertedpropylene, some other low boiling hydrocarbons, and varying amounts ofgaseous products such as nitrogen, carbon dioxide, carbon monoxide andthe like.

Within separator l3 a liquid layer comprising crude acrolein, closeboiling carbonylic impurities, formaldehyde, water, and high boilingorganic material is separated from a gaseousfractlon comprising thenormally gaseous materials as well as substantial amounts of acroleincontaining close boiling carbonylic impurities. The gaseous phase ispassed from separator it through line it into a scrubbing zone. Thescrubbing zone may comprise a scrubbing column l0, optionally containingsuitable packing material, baille plates, or the like. Within column [6the charge thereto is brought into countercurrent contact with asuitable scrubbing medium such as, for example, water, selectivelydissolving or absorbing the acrolein. Water is introduced into the upperpart of column 16 by means of valved line l1. Normally gaseous materialcomprising propylene and fixed gases is eliminated from column it bymeans of valved line l9. Acrolein in admixture with close boilingsaturated impurities such as propionaldehyde, and acetone as well asacetaldehyde and formaldehyde is taken from the lower part of column I6together with the scrubbing water by means of valved line it. s Asuperatmospheric pressure, for example, in the range of from about 50 toabout 500 pounds, and preferably from about 150 to about 250 pounds ismaintained in column iii to assure substantially complete absorption ofthe acrolein. The temperature within column It may range, for example,from about 10 C. to about C. Higher or lower tempera-- acetaldehyde,propionaldehyde and acetone as well as water, is separated from a liquidfraction consisting essentially of water, formaldehyde and high boilingorganic material.

The liquid fraction is taken from stripping column 22 by means of valvedliner" and eliminated from the system. The vapor fraction is takenoverhead from stripping column 22 by means of valved line 26.

The amount of saturated carbonylic impurities contained in the crudeacrolein taken overhead from stripping column 22 through valved line 26will vary considerably often depending upon the specific conditionemployed in producing the crude acrolein. In general the amount of closeboiling carbonylic impurities contained in the crude acrolein passedthrough valved line 26 will not substantially exceed about 10% by weightof the acrolein. It is to be understood. however, that the invention isin no wise limited to the purification of a crude acrolein containingclose boiling carbonylic impurities in any specific amount The watercontent of the crude acrolein overhead from stripping column 22 will beat least equivalent to that of the acrolein-water azeotrope which is2.7% by weight of water based on acrolein. The saturated carbonylicimpurities will generally consist essentially of acetaldehyde,propionaldehyde and acetone in varying amounts.

The following table is illustrative of the comscrubbing and stripping ofoxidation products of propylene as herein described: 7

Per cent by weight Acrolein I '80to 90 Acetaldehyde 3 to 10Propionaldehyde 0.5 to 3 Acetone 1.0to5 High boiling organic material1.0 to2.0 Water 2.4 to 6.0

It is seen that in addition to acetaldehyde the crude acrolein containspropionaldehyde and acetone in contaminating amounts. These saturatedcompounds are not only lower boiling and higher boiling respectively,than acrolein but have boiling temperatures closely approximating thatof acrolein and therefore preclude their separation by ordinarypractical scale fractionating means. It is apparent that the productionof substantially pure acrolein from such a mixture by methods availableheretofore, if feasible at all, necessitates the use of such a pluralityof steps and operations of such complexity as to render itslarge scaleapplication highly impractical. The reduction of its water content belowthe relatively large amount contained in the acrolein-water azeotropenormally obtained in fractionation would occasion the resorttoadditional complex and costly operative steps.

A study oi. the distillation of crude acrolein mixtures in the presenceof polar solvents revealed that whereas the relative volatility (alpha)for the separation of acrolein from acetone is approximately 1.12 in theabsence of a solvent the presence of most polar solvents results in areduction of the relative volatility I value below unity, that isacrolein is the more polar compound and is taken off with the bottoms ofthe column. It was found, however, that water, quite contrary to thebehavior of otherv polar solvents in the presence of acrolein, insteadof decreasing the relative volatility value for the separation ofacrolein from acetone increased it markedly, and that extractivedistillation of crude acrolein in the presence of water resulted in thetaking off overhead of a fraction containing acrolein that was poorer inacetone. Acetaldehyde is also removed to a substantial degree in thebottoms.

The overhead of such an extractive distillation at substantiallyatmospheric or higher pressures will still comprise, however, not only aconsiderable portion of the acetone and acetaldehyde contaminants butwill contain substantially all of the propionaldehyde.

The relative volatility value for the separation of propionaldehyde fromacrolein in the absence of a solvent was found to be about 1.12 andtherefore is separable to at least a substantial degree byfractionation. In the presence of substantial amounts of water it wasfound that the relatively volatility value was increased somewhatattaining a value of about 1.4 in the presence of about 90% of water atatmospheric pressure. A second extractive distillation of the crudeacrolein in the presence of water at substantially atmospheric pressureor higher would therefore enable the removal to some extent ofpropionaldehyde overhead from a crude acrolein mixture. Such a pluralityof steps will, however, occasion a reduction in overall recovery due tolosses caused by hydra-- tion, polymerization etc. Notonly is such aprocess handicapped by the disadvantages inposition of crude acroleinobtained by water herent in the plurality of operative procedures tentof at least 2.7 per. cent by weight based on acrolein, thereby generallynecessitating a further complex dehydration step.

It has now been found, however, that whereas the extractivedistillation, in the presence of water, at substantially atmosphericconditions of the crude acrolein results in the obtaining ofpropionaldehyde in the overhead product, a, lowering of the temperaturebelow a definite critical temperature in the presence of water in anamount at least equal to about 80% by weight of the aqueous mixture,results in the appearance of all of the saturated carbonylic impuritiesincluding, propionaldehyde in the column bottoms leaving substantiallypure acrolein as the sole overhead product. A study has indicated, asgraphically illustrated by the curve A of Figure 11 of the attacheddrawings, that the relative volatility value (alpha) for the separationof propionaldehyde from acrolein in the presence of water not onlyincreases with decrease in temperature but that at the temperature ofabout 35 C. it becomes unity and thereafter increases markedly inpositive value with further decrease in temperature. Thus whereas therelative volatility value for the separation of propionaldehyde fromacrolein in the presence of water is only about'0.71 at a temperature of60 C. it has a value of 1.32 at 20 C. and 2.0 at C.

It has furthermore been found that the low temperature extractivedistillation not only results in the obtaining of a product which issubstantially free of propionaldehyde but which no longer contains thestill considerable amounts of impurities such as acetone, acetaldehydeand water which are comprised in the product obtained at temperaturesabove about 35 C. It was further found, as indicated graphically bycurves B and C, Figure 11 of the drawing, that the values for therelative volatilities for the separation of acetaldehyde and acetone inthe presence of water increased at a markedly rapid rate with'decreasein temperature below about 35 C. Thus whereas these values (alpha) areonly 1.15 and 2.1 at 60 C. for acetaldehyde and acetone, respectively,they are as high as 2 and 4, respectively, at 0 C.

A further signal advantage of the low temperature extractivedistillation resides in the obtaining of acrolein of high puritycontaining substantially less water than that of the acroleinwaterazeotrope obtained at higher temperatures or normal fractionatingconditions. Thus whereas the normal acrolein-water azeotrope containsabout 2.7% of water, the acrolein overhead obtained in the lowtemperature extractive distillation of the invention has a water contentbelow about 0.4%.

The low temperature extractive distillation of the invention thereforeenables the simultaneous separation of all saturated carbonylicimpurities, including those having the same number of carbon atoms tothe molecule as the acrolein, as well as at least a substantial amountof water, from acrolein in a single highly efficient and economicaloperation.

In accordance with the invention the crude acrolein containingacetaldehyde, propionaldehyde, acetone and water is passed from line 26through valved lines 28 and 29 into an extractive distillation zone. Theextractive distillation zone may comprise an extractive distillationcolumn 3| provided with suitable heating means, such as, for example, areboilcr, or a closed heating coil 32. Line 29 is provided with suitablemeans enabling thelntroduction or removal of heat from g the crudeacrolein stream passing therethrough, such as, for example, an indirectheat exchanger 33. The charge may be introduced into the extractivedistillation column 3|. in the liquid, vapor or mixed phase. Within.column 3| the crude acrolein subjected to extractive distillationconditions in the presence of water introduced into the upper part ofthe column by means of valved line 35. Means for controlling thetemperature, of the water introduced into column 31 through valved line35 such as, for example a cooler 35, is provided.

Crude acrolein, comprising acrolein in admixture with one or more closeboiling saturated carbonylic impurities such as, for example, acetone,

propionaldehyde and acetaldehyde may be introduced into the system fromany outside source by means of valved lines 31 and 38 leading into line29. Crude acrolein introduced into the system by means of valved line 31may constitute a part or all of the crude acrolein charge to the system.

Conditions within column 3| are controlled to maintain the temperaturetherein below about 35 C. and preferably below about 20 C. Thus thetemperature within column 3| may be maintained within the broad rangeof, for example, from about 35 C. to about 10 C. and preferably fromabout 20 C. to about 0 C. The temperature within column 3| is maintainedwithin the prescribed range by control of the temperature of thematerials introduced therein and by the maintenance therein ofasufliciently low subatmospheric pressure by any suitable conventionalmeans not shown in the drawing.

Essential to the attainment of the objects of the invention is the.introduction into column 3| of sufiicient water to maintain a singleliquid phase throughout the column. The introduction of water into thecolumn is controlled to maintain the water content of the total mixturetherein at least equal to about by weight. Without intent to limit thescope of the invention by any theories advanced herein to set forth morefully the nature of the invention it is believed that below thetemperature of about 35 C. under the conditions within column 3|,acrolein will not form a hydrate whereas the saturated carbonylicconstituents will undergo hydrate formation. Conditions in column 3| arepreferably controlled within the prescribed conditions 'to obtain athroughput rate assuring attainment of equilibrium with respect to theformation of the hydrates of substantially all of the saturatedcarbonylic compounds introduced into the column. Thus the relativevolatility value for the separation of acrolein from propionaldehydeunder the low temperature extractive distillation conditions was foundto be about 0.71, 1.1 and 1.5 for residence times of 6, 20 and 30seconds respectively. Suitable throughput rates comprise those enablinga residence time per transfer stage of from about 20 to about '75seconds, and preferably from about 25 to about 50 seconds within lowtemperature extractive distillation column 3 I. Aminimum residence timeof about 30 seconds is particularly preferred when effecting the lowtemperature extractive distillation at a temperature of from about 0 C.to about 10 C. Higher minimum residence times may, however, be employedwithin the scope of the invention. The minimum residence time of thecharge within the low temperature extractive distillation column 3|, ithas been found, may be reduced materially bythe acrolein is extractivelydistilled within column 31 with the formation of liquid bottomsconsisting essentially of water, acetaldehyde, propionaldehyde andacetone, and a vapor overhead consisting essentially of acrolein in ahigh state of purity, substantially free of saturated carbonylic stepsas distillation, fractionation and the like,'

to effect the recovery of saturated carbonylic compounds therefrom.

The vaporfraction is taken overhead from column 3| through valved. line4| provided with suitable cooling means such as, for example, acondenser 42, and passed into an accumulator 43. Acrolein in a highstate of purity is drawn from accumulator 43 by means of valved line 44as a final product. A part of the acrolein withdrawn through valved line44 is passed through valved line 45, provided with suitable coolingmeans such as a cooler 46, into the upper part of column 3| at a pointabove that of introduction of the water into the column.

The eiilciency with which acrolein is separated in a high state ofpurity from a crude acrolein obtained by the catalytic oxidation ofpropylene and comprising saturated carbonylic compounds having the samecarbon atoms to the molecule as acrolein is illustrated by the followingexample:

Example I A crude acrolein-containing mixture, obtained a by thecatalytic oxidation of propylene, is subjected to phase separation in aseparator., The

gaseous phase is scrubbed with water at a pres-' sure of about 125 lbs.gauge to recover crudeacrolein therefrom. The rich scrubbing water iscombined with the liquid phase from the separator and subjected todistillation. Crude acrolein is separated as a vapor fraction from aliquid bottoms comprising water, formaldehyde and high boiling organicmaterial. The crude acrolein thus obtained has the followingcomposition:

Weight per cent Acrolein 90.0 Acetaldehyde 6.0 Propionaldehyde 2.0Acetone and is subjected to extractive distillatiofi'in the presence ofwater under the following'lconditions:

Top column temperature, C.'. 9.'7

Reflux to feed ratio The composition of the overhead and bottoms of thecolumn in per cent by weight are indicated in the following table:

Overhead Bottom wt. t.

. Acetaldehyde, having a boiling temperature substantially below that ofacrolein, and a relative volatility of about 3.5 in the absence of asolvent, may be separated to at least a substantial degree from thecrude acrolein by fractionation. In a modification of the invention, theload on the extractive distillation column 3| is reduced by the passageof at least a part of the crude acrolein containing acetaldehyde fi'omline 28 into a fractionating zone. The fractionating zone may comprise asuitable column such as, for example, fractionating column 50.Acetaldehyde-containing crude acrolein, introduced into the systemthrough line 31, may be passed in part or in its entirety into column 50by means of valved line 5|. Within column 50 the crude acrolein issubjected to fractionation to effect the separation of a vapor fractioncomprising acetaldehyde from a liquid fraction comprising acrolein inadmixture with acetone and propionaldehyde.

The vapor fraction is passed overhead from fractionator 50 through line53, provided with cooling means 54, into accumulator 55. Liquidcondensate comprising acetaldehyde is taken from accumulator 55 throughvalved line 58 and eliminated from the system. A part of theliquidpassed through valved line 56 is passed through valved line 5'! asreflux to the top of fractionatpr 50. Such fractionation enables theelimination of at least. a substantialpart of the acetaldehyde from thecharge to the extractive distillation zone as exemplified by thefollowing example:

Example II Crude acrolein obtained by the catalytic oxidation ofpropylene was freed of acetaldehyde by fractionation. The resultingcrude acrolein-containing fractionator bottoms were subjected to a lowtemperature extractive distillation in the presence of water under thefollowing conditions:

Top column temperature, "C -9.l Bottom column temperature, C 16 Topcolumn pressure, mm. Hg abs 50 Bottom column pressure, mm. Hg abs. 152Water content of column percent by weight of total liquid on trays incolumn 83 Reflux ra i 2 Composition of the. crude-acrolein charge andthe products of the distillation are indicated in th following table:

Extractive Distillation Crude was Feed Botfmcfiom toms from anon CrudeOverhead Bottoms Fractionator 102.7 wt? 10!.7 wt.'7 Acroleiu 03 059705.4 3.10 Propionaldehyde. 2. 0 2. 16 0. 2 0. 2i Acetone 2. 0 2. 15 0. 00. 23 Aoetaldehyde.-. 6. 0 0. 2 0. 0 02 Water I 0. 4 99. 40

1 1 Although the detailed description of the invention has stressed thepurification of crude acrolein containing both acetone andpropionaldehyde it is to be understood that it may be applied to theseparation of acrolein from mixtures containing Example III A mixture ofacrolein and propionaldehyde, containing" 2.0% by weight ofpropionaldehyde is extractively distilled at low temperature in thepresence of water. A temperature of 4 C. and a pressure of 62 mm. Hgabs. are maintained in the upper part of the extractive distillationcolumn and a temperature of C. and a pressure of 152 mm. Hg abs. in thelower part of the column. A reflux ratio of 2 is employed. Water iscontinuously introduced into the upper part of the column, below thepoint of introduction of reflux, in sufficient amount to maintain aratio of water to feed charged to the column of 9.8. 99% of the acroleincharged is recovered in the column overhead as acrolein of 99.3% purity.

Example IV A mixture of acrolein and acetone, containing 2% by weight ofacetone is extractively distilled at low temperature in the presence ofwater. A temperature oi 0 C. and a pressure of 62 mm. Hg abs. aremaintained in the upper part of the extractive distillation column and atemperature of C. and a pressure of 150 mm. Hg abs. in the lower part ofthe column. A reflux ratio of 2.0 is employed. Water is continuouslyintroduced into the upper part of the column, at a point below theintroduction of reflux in suflicient amount to maintain a ratio of waterto feed charged of 9.8, 99% of the acrolein charged was obtainedoverhead from the column as acrolein of 99.7% purity.

The process of the invention thus not only enables the large scaleproduction of acrolein from crude acrolein, such as obtained for exampleby the catalytic oxidation or propylene, in a substantially higher stateof purity than possible by practical scale methods disclosed heretoforebut makes possible its production with markedly improved efllciency.

Although the illustrative description of the invention has stressed theseparation of acrolein from saturated carbonylic compounds the inventionmay be applied to the separation of unsaturated aldehydes other thanacrolein from saturated carbonylic impurities having boilingtemperatures closely approximating that of the unsaturated aldehyde. Theinvention is applied with particular advantage to the separation ofalpha-beta unsaturated aldehydes from the crude unsaturated aldehydesobtained by the oxidation of the corresponding hydrocarbons. Thus theinvention may be applied to the separation of methacrolein fromadmixture with acetalde- 1. The process for separating acrolein in ahigh state of purity from a mixture comprising acrolein in admixturewith propionaldehyde which comprises extractively distilling saidmixture at a temperature below 35 C. in the presence of a suflicientamount of water to maintain substantially a single liquid phase in theextractive distillation zone, thereby separating a vapor fractionconsisting essentially of acrolein free of any substantial amount ofpropionaldehyde from liquid bottoms comprising water and propionaldehydein the extractive distillation zone.

2. The process for separating acrolein in a high state of purity from amixture comprising acrolein in admixture with propionaldehyde whichcomprises extractively distilling said mixture at a temperature aboveabout -10 C. and below 35 C. in the presence of a suflicient amount ofwater to maintain substantially a single liquid phase in the extractivedistillation zone, thereby separating a vapor fraction consistingessentially of acrolein free of any substantial amount ofpropionaldehyde from liquid bottoms comprising water and propionaldehydein the extractive distillation zone.

3. The process for separating acrolein in a high state of purity from amixture comprising acrolein in admixture with propionaldehyde whichcomprises extractively distilling said mixture at a temperature of fromabout 0 C. to about 20 C. in the presence of a sumcient amount of waterto maintain substantially a single liquid phase in the extractivedistillation zone, thereby separating a vapor fraction consistingessentially of acrolein free of any substantial amount ofpropionaldehyde from liquid bottoms comprising water and propionaldehydein the extractive distillation zone.

4. The process for separating acrolein in a high state of purity from amixture comprising acrolein in admixture with propionaldehyde andacetone which comprises extractively distilling said mixture at atemperature above about l0 C. and below 35 C. in the presence of asufficient amount of water to maintain substantially a single liquidphase in the extractive distillation zone. thereby separating a vaporfraction consisting essentially of acrolein free of any substantialamount of propionaldehyde and acetone from liquid bottoms comprisingwater, propionaldehyde and acetone in the extractive distillation zone.

5. The process for separating acrolein in a high state of purity from amixture comprising acrolein in admixture with propionaldehyde andacetone which comprises extractively distilling said mixture at atemperature of from about 0 C. to about 20 C. in the presence of asufllcient amount of water to maintain substantially a single liquidphase in the extractive distillation zone, thereby separating a vaporfraction consisting essentially of acrolein free of any substantialamount of propionaldehyde and acetone from liquid bottoms comprisingwater propionaldehyde and acetone in the extractive distillation zone.

6. The process for separating acrolein in a high state of purity fromcrude acrolein comprising acrolein in admixture withpropionaldehyde-containing saturated carbonylic compounds having thesame number of carbon atoms to the molecule as acrolein, which comprisesextractively distilling said crude acrolein at a temperature below 35 C.in the presence of a sufficient amount of water to maintainsubstantially a single liquid phase in the extractive distillation zone,thereby" separating a vapor traction consisting essentially of acroleinfree or any substantial amount of saturated carbonylic compounds fromliquid bottoms comprising water and said saturated carbonylic compoundsin the extractive distillation zone.

7. The process for separating acrolein in a high state of purity fromcrude acrolein com- I prising acrolein in admixture withpropionaldehyde-containing saturated carbonylic compounds having thesame number of carbon atoms to the molecule as acrolein which comprisesextractively distilling said crude acrolein at a temperature of fromabout -1 0, C. to about 20 C. in the presence of a suflicient amount ofwater to maincomprising acrolein in admixture with close boilingsaturated carbonylic impurities, which comprises extractively distillingsaid crude acrolein at a temperature of from about -l C. to about 20 C.in the presence of a sufficient amount of water to maintainsubstantially a single liquid phase in the extractive distillation zone,thereby separating a vapor fraction consisting essentially of acroleinfree of any substantial amount of saturated carbonylic compounds fromliquid bottoms comprising water and said saturated carbonylic compoundsin the extractive distillation zone.

9. The process for the separation of an alphabeta unsaturated aliphaticaldehyde having from three to four carbon atoms to the molecule in ahigh state of purity from a mixture comprising said alpha-betaunsaturated aldehyde having from three to four carbon atoms to themolecule in admixture with a saturated aldehyde having the same numberof carbon atoms to "the molecule as said unsaturated aldehyde whichcomprises extractively distilling said mixture at subatmosphericpressure and at a temperature below 35 C. in the presence of asufiicient amount of water to maintain a single liquid phase in theextractive distillation zone.

10. The process for separating an alpha-beta unsaturated aliphaticaldehyde having from three to four carbon atoms to the molecule from acrude alpha-beta unsaturated aliphatic aldehyde having from three tofour carbon atoms to the molecule obtained by the oxidation of thecorresponding olefin, said crude unsaturated aldehyde comprising saidalpha-beta unsaturated aldehyde in admixture with saturated carbonylicimpurities having the same number of carbon atoms to the molecule assaid unsaturated aldehyde, which comprises extractively distilling saidcrude unsaturated aldehyde at subatmospheric gaseous hydrocarbons,formaldehyde, acetaldehyde, acetone, propionaldehyde and high boilingorganic impurities, which comprises scrubbing said reaction productswith water at superatmospheric pressure to obtain a rich scrubbingmedium comprising water and said reaction products substantially free ofnormally gaseous hydrocarbons, distilling said rich scrubbing medium toseparate crude acrolein comprising acrolein in admixture withpropionaldehyde and acetone therefrom, and extractively distilling saidcrude acrolein at a temperature below 35 C. in the presence of asuflicient amount of water to maintain substantially a single liquidphase in the extractive distillation zone, thereby separating a vaporfraction consisting essentially of acrolein free of any substantialamount of propionaldehyde and acetone from liquid bottoms comprisingwater, propionaldehyde and aceton in the extractive distillation zone.

12. The process for purifying crude acroleincontaining reaction productsobtained by the oxidation of propylene, said reaction productscomprising acrolein in admixture with normally gaseous hydrocarbons,formaldehyde, acetaldehyde, acetone, propionaldehyde and high boilingorganic impurities, which comprises separating a fraction consistingessentially of crude acrolein comprising acrolein in admixture withpropionaldehyde and actone from said reaction products, and extractivelydistilling said crude acrolein at a temperature of from about -10 C. toabout 20 C. in the presence of a sufficient amount of water to maintainsubstantially a single liquid phase in the extractive distillation zone,thereby separating a vapor fraction consisting essentially of acroleinfree of any substantial amount of propionaldehyde and acetone fromliquid bottoms comprising water, propionaldehyde and acetone in theextractive distillation zone.

13. The process for purifying crude acrolein-. containing reactionproducts obtained by the oxidation of propylene, said reaction productscomprising acrolein in admixture with normally gaseous hydrocarbons,formaldehyde, propionaldehyde-containing saturated carbonylic compoundshaving boiling temperatures closely approximating that of acrolein, andhigh boiling organic impurities, which comprises scrubbing said reactionproducts with water at superatm'ospheric pressure to obtain a richscrubbing medium comprising water and said reaction productssubstantially free of normally gaseous hydrocarbons, distilling said'rich scrubbing medium to separate crude acrolein comprising acrolein inadmixture with close boiling saturated carbonylic impurities therefrom,and extractively distilling said crude acrolein at a temperature below35 C. in

. eous v hydrocarbons, formaldehyde, propionaldehyde-containingsaturated carbonylic compounds having boiling temperatures closelyapproximating that of acrolein and high boiling organic impurities,which comprises separating a fraction consisting essentially of crudea'crolein comprising acrolein in admixture with said close boilingsaturated carbonylic compounds from said reaction products, andextractively distilling said crude acrolein at a temperature of fromabout C. to about 20 C. in the presence of a suiiicient amount of waterto maintain substantially a single liquid phase in the extractivedistillation zone, thereby separating a vapor fraction consistingessentially of acrolein free of any substantial amount of said closeboiling saturated carbonylic compounds from liquid bottoms comprisingwater and said saturated carbonylic compounds in the extractivedistillation zone.

15. The process for purifying crude acroleincontaining reaction productsobtained by the oxidation of propylene, said reaction productscomprising acrolein in admixture with normally gaseous hydrocarbons,saturated carbonylic impurities substantially lower boiling thanacrolein comprising formaldehyde and acetaldehyde, saturated carbonylicimpurities having boiling temperatures closely approximating that ofacrolein comprising propionaldehpde, and high boiling organicimpurities, which comprises scrubbing said reaction products with waterat superatmospheric pressure to obtain a rich aqueous scrubbing mediumcomprising water and said reaction products substantially free ofnormally gaseous hydrocarbons, distilling said rich scrubbing medium toseparate crude acrolein comprising acrolein in admixture with said closeboiling saturated carbonylic impurities comprising propionaldehydetherefrom, and extractively distilling said crude acrolein at atemperature below 35 C. in the presence of a suflicient amount of waterto maintain a single liquid phase in the extractive distillation zone,thereby separating a vapor fraction consisting essentially of acroleinsubstantially free of any saturated carbonylic impurities from liquidbottoms comprising water and saturated carbonylic impurities comprisingpropionaldehyde in the extractive distillation zone.

16. The process for the purification of crude acrolein-containingreaction products obtained by the oxidation of propylene, said reactionproducts comprising acrolein in admixture with normally gaseoushydrocarbons, saturated carbonylic impurities substantially lowerboiling than acrolein comprising formaldehyde and acetaldehyde,saturated carbonylic impurities having boiling temperatures closelyapproximating that of acrolein comprising propionaldehyde, and highboiling organic impurities, which comprises separating a fractionconsisting essentially ofcrude acrolein comprising acrolein in admixturewith said close boiling saturated carbonylic impurities comprisingpropionaldehyde from said reaction products, and extractively distillingsaid crude acrolein at a temperature of from about 10 C. to about 20 C.in the presence of a sufilcient amount of water to maintain a singlephase in the extractive distillation zone, thereby separating a vaporfraction consisting essentially of acrolein substantially free of anysaturated carbonylic impurities from liquid bottoms comprising water andsaid saturated carbonylic impurities comprising propionaldehyde in theextractive distillation zone.

GINO J. PIEROTTI. ARTHUR E. HANDLOS. CHARLES M. REIDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,033,539 Ralston et al Mar. 10,1936 2,179,991 Bright et a1 Nov. 14, 1939 2,198,651 Bludworth Apr. 30,1940 2,261,704 Wagner -Nov. 4, 1941 2,283,911 Brant et al May 26, 19422,290,636 Deanesly July 21, 1942 2,334,091 Herstein Nov. 9, 19432,341,748 Hopkins June 15, 1943

10. THE PROCESS FOR SEPARATING AN ALPHA-BETA UNSATURATED ALIPHATICALDEHYDE HAVING FROM THREE TO FOUR CARBON ATOMS TO THE MOLECULE FROM ACRUDE ALPHA-BETA UNSATURATED ALIPHATIC ALDEHYDE HAVING FROM THREE TOFOUR CARBON ATOMS TO THE MOLECULE OBTAINED BY THE OXIDATION OF THECORRESPONDING OLEFIN, SAID CRUDE UNSATURATED ALDEHYDE COMPRISING SAIDALPHA-BETA UNSATURATED ALDEHYDE IN ADMIXTURE WITH SATURATED CARBONYLICIMPURITIES HAVING THE SAME NUMBER OF CARBON ATOMS TO THE MOLECULE ASSAID UNSATURATED ALDEHYDE, WHICH COMPRISES EXTRACTIVELY DISTILLING SAIDCRUDE UNSATURATED ALDEHYDE AT SUBATMOSPHERIC PRESSURE AND AT ATEMPERATURE BELOW 35*C. IN THE PRESENCE OF A SUFFICIENT AMOUNT OF WATERTO MAINTAIN SUBSTANTIALLY A SINGLE LIQUID PHASE IN THE EXTRACTIVEDISTILLATION ZONE.